Pros: Clarity, resolution, detail, smoothness, deep bass that is in general tight and well controlled, very easy to power, great quality cable, value.
Cons: Slight bass resonance, slighlty "off" tonality in the mids, highs can be sibilant sometimes, too big and bulky, resulting in loose fit.
When I bought these headphones about 2 months ago, I didn't expect much and I bought them without trying them out. It was an impulse buy to be honest, they were on a considerable discount and I just could not resist it.
Having no previous experience with Denon headphones (what I know about them came from reading the reviews of the old Dx000 series), and looking at the box design, I expected a bass heavy, V-shaped, "modern sounding" headphones designed for modern music, not really an audiophile grade sound. I'm happy to say I was pleasantly surprised.
PACKAGING & ACCESSORIES:
The headphones come in a hard cardboard box, the inside lined with black foam and bronze colored silky cloth. Headphones are well protected inside during transport and there's no risk of damage. It comes with a carrying bag that feels sort of small for the D600's, it's the exact same bag that comes with cheap Denon's from the new D series, I would personally never use it, but I guess it's all right.
The headphones come with two cables, one short, thin, rubbery and cheap feeling cable with an Apple remote on it that probably nobody will ever use, and the other, long, thick, high quality braided cable. It really is a high quality feeling cable, very soft, doesn't tangle at all and it has nice high quality gold plated jacks on the ends, with the 3.5mm stereo jack made out of aluminium. Probably the nicest cable of any headphone I've owned so far.
BUILD & COMFORT:
These headphones are made mostly out of plastic. Apart from the metal inside the headband and the round aluminium plates on the sides of the earcups with Denon written on it, everything is made out of plastics. It's pretty solid, and might fool you to think it's metal at first since it's strangely cold to the touch and has metalic texture to it, but it's plastic. But because of that they're fairly lightweight relative to their huge size. As far as the actual build quality goes, it's good, they feel solid, there's no rattling, no squeaking, headband adjustment mechanism operates smoothly (even though it's a bit too loose when headband is not stretched apart).
Earpads and headband are covered with protein leather which looks and feel real, it's very smooth and soft and has a premium feel to it. Actual pads are made out of memory foam and they're extremelly soft, and the same is true for the headband which never feels like it ran out of padding.
The comfort of these headphones is generally good. I say generally because it does have a few issues. Headband is soft, earpads are soft and very big, the earcup is very deep and has plenty of room in all directions even for my huge ears. There is also no problem with wearing glasses while using the headphones since the earpads are so soft.
The issue with comfort is actually in the size and fit. The headphones are HUGE, they look ridiculous on the head, and even though they're lighter than you'd think, they're still heavier than most full-size headphones. Also, they don't fit well. They're not uncomfortable to wear, but they don't fit like a glove like some other headphones do...like Beyerdynamics for example. The clamping force on the D600's is virtually non-existent, combine that with their weight and size, and they don't feel secture on the head, and that is something that I hate. Not being able to move my head freely because headphones will move as well and ruin the seal / change the sound is not good. These are definetly headphones that you put on your head and sit still in a comfy chair while listening to music.
I'm not saying these are uncomfortable headphones, but to me, high comfort doesn't just mean soft earpads, but perfect fit and feel. For example, Beyerdynamic T1's feel like a tailored suit, you put them on, and they feel like they're made for your head, they feel incredibly light even though they're actually heavies than D600's (that's because they have a very low profile, close to the head), very comfy and don't feel like a huge piece of hardware on your head, but like a part of you. That is very important for psychoacoustics as well, and ignored by a lot of people. You'll never really get lost in the sound if the headphones constantly remind you they're on your head.
This is the interesting part. As I said, I expected a V-shaped modern sound, but actually got something completely different.
These headphones are fairly neutral sounding. Yes, they do have a somewhat elevated bass, and yes, the highs are slightly above neutral as well, but they're still within the borders of what can be considered neutral. Since I've used them quite a lot in combination with T1's, and they're sort of similar in some ways, I'm going to compare them in some aspects as well.
The bass extends really deep, it's flat sounding, there's no bumps or dips in the bass response and it's well textured for a closed back headphones. It's slightly elevated relative to the midrange, but only enough to give it some more life. It never feels like it's overwhelming the rest of the sound, and it's well separated from the mids. However, as with almost any closed back headphones, it does suffer from some minor mid-bass resonance. If this was a cheap headphone, you would not notice it, since the rest of the sound would not be clean enough to highlight the problem, but when the mids and highs and as clear as on the D600's, this resonance and slight lack of tightness can sometimes be a minor problem, but in general bass is fairly quick and well behaved and most of the time tight and solid. When playing some really punchy bass at really high volumes, there is some minor distortion to it, but not due to drivers, but due to earcups. It's actually a "boooiiingggg" sound that you can hear after the bass hits, but it's only really present on extreme volumes that nobody is going to listen at.
Mids are very clean and clear sounding. There's just a sense of purity and resolution in the mids that feels great and give a good "you're there" sensation for closed back headphones. They're very vivid and colorful sounding. These are not headphones that nail the tonality, as they can sound slightly nasal and slightly "wrong" in terms of tonality sometimes (out of the box the problem is much more present than after some running in), but in general, the mids are very, very detailed, well textured and transparent enough for the price of the headphones and their closed type. They can feel ever so slightly thin sometimes, but you can't have it all.
Highs are again very slightly elevated, but very clean, fast and sparkly sounding, with none of that metallic tizzy sound, even though they can be very slighlty sibilant with some recordings. Again, not exactly perfectly natural sound in terms of tonality, maybe slightly "enchanced" to make it sound more hi-fi, but it works and the general sense is the same as with the mids. What strikes you first is the amount of clariry and resolution in the sound, and how vivid and engaging the sound is because of it. Detail is also exceptional. In fact, these are the first headphones that I've bought in the last year that actually made me hear things in recordings that I've never heard before, and among all those headphones are T1's as well. I'm not saying the D600's are more detailed than T1's, but their "enhanced clarity" makes it feel that way and microdetail in music pops out more clearly. When I heard those news pops and crackles in the music with D600's, I switched to T1's and could hear it as well, but I had to really focus on it, while with D600's it would just pop out. It's the same as the case of HD650 vs K701. K701's are not more detailed, but you can hear those details more clearly and focus on them more easily. The good thing is, D600's manange to do that in a very musical fashion. They do not sound like analytical headphones at all, they are fun and musical, yet their levels of detail and resolution surpasses a lot of headphones that do sound analytical. DT880's come to mind here as well.
Soundstage and imaging are impressive for closed back headphones. They don't have the depth or the frontal projection of the sound up the levels of the T1's, but the width and height of the soundstage is comparable, if not superior to the T1's in the sense of creating an atmosphere around you. This is really good in movies and you can tell Denon knows what they're doing when it comes to that, having loads of experience when it comes to home theaters. Imaging is great for closed back headphones at this price, superior to something like DT880's or K701's and definitely a good few steps ahead of the DT770 80's and M50's , but clearly behind T1's. When I say clearly I don't mean that D600's are crushed by the T1's, but the imaging is not as good, although it never feels like it's lacking. It's only after I switch to the T1's that I notice a new level of coherence and precision in the placement of various sounds that was not present before. Still, very impressive for closed back headphones at this price.
Because of the slightly elevated highs and a slightly "off" tonality in the mids though, as well slight resonance in the mid-bass sometimes, they lack the coherence and smoothness of really good open-back headphones. They don't have the coherency and don't put all the elements of music together with as much finesse, and they don't separate the sounds quite as good as equally priced open back headphones. They're not as effortless to listen to.
These are still very smooth sounding headphones, there's no audible harshness, but it's still clear that these are not flagship headphones. Compared to flaghsip headphones such as the T1's that becomes clear after some more focused listening. Even though they're smooth, musical and atmospheric sounding, they're still a step behind the T1's in all those terms. What I'm about to say might make the D600's look bad, but taking them off and putting T1's on feels like a relief on the ears. The sound of the T1's flows in such an effortless manner that it's clear they're superior headphones. Again, technically looking, in terms of resolution, clarity and detail, there's not much between the two, they're pretty even with T1's being ever so slightly ahead, but in terms of their presentation, D600's are behind a step. Still, very good compared to other similar headphones and I don't want this unfair comparison with the T1's to ruin your view of the D600's.
In general, if I were to describe the sound in a few words, it would be: clear, pure, very detailed, very high resolution, spacious. These are the things that I notice first and strike the strongest impression when I put them on, and again, in those categories they hold their own against even the T1's. After some time, slight sibilance in the highs, slight resonance in the bass and sometimes a slight nasal quality of the mids can be noticed in some music when switching between them...but then again, T1's nail the tonality, so almost everything sounds slightly wrong when directly compared to them, so take this with a grain of salt. When you adjust to the D600's after some time, they sound perfectly natural and believable, and have a good atmosphere and "you're there" feel to them.
AMPING: This is a category that might potentially make these headphones winners. The thing is, these headphones are EXTREMELLY easy to run. Literally, plug them into RCA outputs of your DAC trough a RCA-->3,5mm adapter, control the volume digitally from your PC, and they sound as good as they can. Plug them into an iPhone, and they sound amazing. In fact, I prefer the sound of them plugged into an iPhone 4S than when they're used with the Musical Fidelity M1DAC and M1HPAP, which is a close to 2000 dollar combo. They sound tigher and more coherent out of an iPhone, less juice that makes them ever so slighlty leaner on the bass might be the reason.
Of course they can play louder out of an amp, but they go plenty loud without an amp, and they do sound a tiny bit more open and full, but nothing even remotely worth paying close to 2000 dollars for...not even 100, that's how small the difference is. They also play equally good out of high output impedance sources such as integrated amplifier headphone outputs. The high output impedance doesn't seem to bother them at all and there are no noticable changes in sound when plugging them into an Onkyo A-5VL amp, which suggests they have a flat impedance/frequency curve.
This is the thing....that's what makes these headphones cheaper than they actually are, because you're only paying for the headphones, not the headphones and a setup to go with it. As long as you have a smartphone, receiver, integrated amp, a DAC or a decent soundcard, you're at 95% of their potential and not losing out anything major if you don't have a separate headamp.
All in all, very good headphones. Their biggest flaws are size, loose fit, slight nasal quality to the mids, slight resonance in the mid bass when playing really bass heavy music at really high volumes, and slightly "enchanced" highs that can sometimes increase the amount of sibilance and give some listening fatigue (which is in general low) rather than more detail.
One last thing to note is that these are one of the few headphones where I actually noticed a significant change in the sound during running in. First 10 hours are critical.